Rebuilding Bones Stronger and Faster with Titanium Foam

The new titanium foam better imitates the structure of natural bone. Image by Fraunhofer IFAM.

I have a half-dozen titanium plates in my right forearm. They connect a bone graft taken from my left leg to the upper part of my radius and to my wrist. This system isn’t perfect, but it does the job.

When my arm snapped, the lower half of my radius shot out my body; it couldn’t be found, let alone repaired. A full titanium rod would have been stiff, wouldn’t have bonded with the existing bone, and would have been harder to arrange muscles and tendons and nerves and blood vessels around as my arm was rebuilt. Solid metal just isn’t light, porous, malleable like bone. Using an existing bone, from my own body, with its own blood supply, was the surer path to giving my arm some functionality again. So orthopedic surgeons removed my fibula — the thin, “chicken-leg” bone next to the shin that isn’t necessary for walking or even running in humans — and carved it up to make a replacement. Titanium keeps everything together, but it’s not doing most (hardly any) of the structural work.

In many cases, though, this isn’t an option: bone grafts from either the fibula or any other site are the wrong size, shape, or density to be used to strengthen or replace a fractured or missing bone. That’s why surgeons still use titanium rods. Solid metal isn’t as good as bone, but at least it’s as strong as bone.

But what if the titanium were actually structured like bone? Instead of a rod, a foam — strong yet flexible, solid yet porous, composed of a metal alloy but otherwise as similar to bone as possible?

Fraunhofer, a German industrial and medical research firm, has actually created such a substance with their TiFoam project. The titanium foam has a complex internal structure that allows blood vessels and existing bone cells to grow into the foam, integrating them into its own matrix (and vice versa). This makes the foam particularly useful to repair damaged bones that are still partially intact, like the radius in my arm.

For constructing bone replacements or prosthetics, the Titanium foam serves a slightly different function; it become more or less dense as the weight-bearing requirements of the substitute bone demand — meaning, for instance, that a fingertip bone doesn’t need to be as heavy per cubic inch as a femur.

Finally, titanium foam allows for stress to be replaced on the repaired bone immediately. In fact, it requires it: only load-bearing stress can trigger the proper density formation of the graft and integration of the existing bone with the foam, fostering faster and more substantive healing.

On this project, Fraunhofer worked with researchers at the technical university of Dresden, and medical manufacturers InnoTERE; InnoTERE had already announced that they are beginning to develop and produce TiFoam-based bone implants.